In certain cutting operations performed by rotary cutting tools, for example, the finishing of a rough-bored hole, the drilling of a hole with a drill-jig bushing to guide the cutting tool or the formation of a thread in a rough-bored hole, special toolholders are required for attaching the cutting tools to machine spindles for rotating the tools. Known and conventional toolholders for such cutting operations have a joint-type coupling between the driving and driven parts thereof to permit angular adjustment of the position of the cutting tool relative to the spindle. These conventional joint coupling toolholders permit the axis of the driven part to be inclined relative to the axis of the driving part. The relative angular adjustment of the axes of the driven and driving parts are intended to allow the driven part to adapt itself to the drilling axis defined by the rough-bored hole or the drill-jig bushing.
Various constructions have been used for toolholders to permit this angular adjustment. However, these conventional devices have not been capable of accurately matching the particular hole being cut despite the pivotal or angular adjustment provided by the joint coupling of the toolholder and despite the capability of changing the pivotal axis of the joint coupling relative to the hole being cut. Adjustment of the pivoting axis relative to the hole generally makes the angle of the driven part relative to the driving part smaller. If the cutting tool is not accurately positioned to match the particular hole being cut, the hole axis is modified or there is a jamming of the cutting tool in the hole or drill-jig bushing. Both instances result in undesirable effects, such as increased wear on the tooling and remachining of the tool. Although this problem associated with conventional machinery may be reduced to some extent by making the machine spindle which drives the toolholder also pivotable, such modification of the machine spindle significantly increases the costs and complexity of the machine spindle.